The heating of water in coffee machines is achieved by means of encased resistors, wherein the resistance wire is generally spiral-wound inside a casing. Furthermore, in flow heaters the encased resistor is also typically associated to a tubular duct in which water circulates, so that the respective axes of longitudinal development are parallel to each other.
The duct and the encased resistor thus associated can be arranged, for example spiral-wound, inside a coffee machine to limit the dimensions thereof and so that a tubular duct has the resistor placed side by side on two opposite sides, thus improving the heat exchange.
It is also requested that the heater take on extreme forms in terms of bending angles so that it may adapt to the shape of the domestic appliance.
For this reason the brazing procedure cannot be performed prior to the bending/winding of the resistor since it would be deteriorated by the subsequent bending/winding of the resistor.
On the other hand, it is requested that the amount of brazing material be minimized and the operation be simplified since said operation becomes complicated when the heater is already bent/wound in its final form. It is therefore fundamental to optimise the coupling between the encased resistor and the tubular fluid circulation duct.
WO2007/135519 describes a solution wherein one support element simultaneously defines the encased resistor and the tubular duct for the passage of the liquids. Said solution presents the disadvantage of having to subject the heater to costly cutting and turning operations at the ends since the ends of the fluid circulation ducts must emerge with respect to the terminals of the resistor and must be especially shaped/machined to allow suitable connections to be fitted to the hydraulic circuit of the domestic appliance or coffee machine. Thus, although this solution eliminates or reduces brazing of the resistor, it presents the disadvantage of complicating machining on the ends of the fluid circulation duct.